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Fire is a regular feature of the Australian outback and the current
severity is at least partly due to humans trying to side-step natural
processes. (OK, climate change and drought come into to, but they too are
not without human inputs)

Given that fire is part of the ecosystem cycle it seems likely that
Australian fungi will have evolved coping strategies, tho they might
struggle after the severity of recent events.

Turning to the UK: fire is (or was - for similar reasons) part of the
heathland cycle so heathland fungi cope quite well. (Of course heathland is
a post industrial landscape and not really natural).

There are two questions really:
1. do fungi survive fire or reinvade afterwards?
If the former the severity might be a problem, if the latter, probably less
so.

2. would sufficient organic matter survive the fire to support fungal
growth?
Fierce fires burn deeper into the soil (esp in drought conditions) and
there’s no charred biomass left behind for colonisation, so this is likely
to be a problem.

Of course if you get down to the mineral soil, the volatile organic and
nitrogen-based plant nutrients will have gone and the inorganics will be
reduced to oxides, many of which are soluble and will wash out in the first
rain - so you’re left with very infertile (low N,P,K) soil and the
succession will start from scratch: lichens, mosses (with their associated
fungi), higher plants will eventually establish when there’s enuf
accumulated biomass for their mycorrhizal fungi survive.